1. Field of Invention
This invention relates to low-firing, high durability glass and enamel compositions. In particular, the invention relates to glass frit compositions, and the glasses, ceramics and enamels made therefrom, which include SiO2, alkali metal oxides, alkaline earth metal oxides, tin oxide and copper oxide. The compositions possess a red color achievable without the use of cadmium, lead, or chromium. The compositions may be used to form red-colored articles or as pigments on substrates such as glass, enamels, metals, and even as colorants in thermoplastics.
2. Description of Related Art
Coloration of glasses, enamels, metals and plastics with a red color has presented an especially difficult challenge for skilled practitioners. Traditionally, one or more of the oxides of iron or lead or chromium or sulfides of cadmium have been used to impart a red color to such substrates. For example, iron oxide, Fe2O3, lead oxide Pb2O3, and cadmium selenium sulfide ((Cd, Se)S), and such as molybdenum chromium red, or pigment red 104. However, iron oxides often have unwanted side effects, and heavy metals such as lead, chromium (especially hexavalent chromium), cadmium and selenium have come under increasing scrutiny from environmental agencies.
Further, most of the aforementioned red-tone pigments impart a relatively brownish color that often overwhelms the true red color often desired. There has been a dearth of truly deep vivid reds in the glass and enamels industry as well as in the thermoplastic industry.
Accordingly, and in particular, the goal of this work is to stain reduced-tin frits with copper to produce red pigments. Since cadmium is considered to be a heavy metal, replacing cadmium-containing pigments with cadmium-free pigments has long been an objective of the glass industry.